With continuous growth of a user's requirement for bandwidth, a conventional copper wire broadband access system is increasingly confronted with a bandwidth bottleneck. At the same time, an optical fiber communications technology with a massive bandwidth capacity is increasingly mature, and an optical fiber access network becomes a strong competitor of a next-generation broadband access network. In particular, a PON (passive optical network) system is more competitive.
In the PON system, an optical module is used as a physical entity for implementing a transceiver system, and a function of the optical module is of great importance; a laser is used as a transmission apparatus of a communication lightwave, a function of the laser is a top priority. In many application scenarios of a PON field, a transmit wavelength of a laser device needs to be stable at a specific value, so as to ensure that technical specifications of physical transmission and an optical communication standard are met. Therefore, in many application scenarios, a laser in an optical module generally has a semiconductor cooler or a heating membrane used to adjust a wavelength, and a laser wavelength monitoring apparatus needs to be used to implement a feedback adjustment.
As shown in FIG. 1, a prior laser wavelength monitoring apparatus includes a collimation lens 1, a first focusing lens 2, an F-P etalon 3, two beam splitters 4a and 4b, two optical receivers 5a and 5b, and two second focusing lenses 6a and 6b, where the F-P etalon 3 functions as a comb filter, and the two beam splitters 4a and 4b each are a beam splitter that has a fixed split ratio. Light emitted by a laser 7 becomes collimated light after passing through the collimation lens 1. The beam splitter 4a divides the collimated light according to a specific ratio, where one part of the light is received by the optical receiver 5a after passing through the second focusing lens 6a, and the other part of the light is incident into the F-P etalon 3 after passing through the beam splitter 4a. The beam splitter 4b divides, according to a specific ratio, light that penetrates the F-P etalon 3, where one part of the light is received by the optical receiver 5b after passing through the second focusing lens 6b, and the other part of the light passes through the beam splitter 4b, and then is incident into an incident port 8 of a transmit fiber after passing through the first focusing lens 2.
It is assumed that PD10 and PD20 are respectively initially calibrated optical powers of the two optical receivers 5a and 5b, PD1 and PD2 are respectively actual received optical powers of the two optical receivers 5a and 5b, and a ratio of the actual received optical power of the optical receiver 5b to that of the optical receiver 5a is A=PD2/PD1. When a redshift occurs in a laser wavelength, PD2=PD20+ΔP, and when a blueshift occurs in the laser wavelength, PD2=PD20=ΔP; PD1 does not vary with the laser wavelength. Therefore, a wavelength offset is:ΔA=+ΔP/PD10 (redshift), and ΔA=−ΔP/PD10 (blueshift)  (1)
Therefore, a change status of a laser wavelength may be defined according to the wavelength offset ΔA.
The inventor of the present patent application finds that because of two beam splitters, an overall packaging size of a laser wavelength monitoring apparatus is relatively large, and packaging costs are relatively high, which does not accord with a current development tendency of miniaturization and low costs. In addition, monitoring precision of a laser wavelength monitoring apparatus of this structure is not high enough.